1. Field of the Invention
The present invention relates to an image pickup apparatus for picking up a scene with an image sensor and storing the resulting image signal. More particularly, the present invention relates to an image pickup apparatus capable of picking up a plurality of successive pictures in a continuous shoot mode.
2. Description of the Background Art
A digital still camera extensively used today uses a CCD (Charge Coupled Device) image sensor or similar solid-state image sensor in place of the traditional silver halide photosensitive type of film. This kind of camera is capable of storing image data output from the image sensor in a semiconductor memory or similar storage and reproducing it on a monitor in the form of a picture. This allows the operator of the camera, watching the monitor, to confirm the result of a shot immediately after the shot. However, it is not easy for the operator to determine a shutter chance while focusing the camera on a desired subject and selecting the range of a shot at the same time, and then pick up the scene at a desired timing. For example, the operator is apt to miss a shutter chance due to the delay of operator's decision or action or the delay of operation particular to the camera. This brings about a release time lag between the intended time for shooting and the time of the actual shot.
In light of the above, Japanese patent laid-open publication No. 205605/1997 discloses an image pickup system including an image pickup apparatus and a computer connected to each other. Image data generated by the image pickup apparatus earlier than the input of a shoot command by a period of time corresponding to the release time lag is input to the computer. The system measures a release time lag particular to the operator of the apparatus and includes a memory capable of storing image data to be picked up over the time lag. When the operator operates a shutter release button of the camera, image data representative of the oldest picture existing in an image buffer of the camera is displayed and written to an auxiliary memory.
The release time lag, however, depends on the person to operate the image pickup apparatus. The prior art system, therefore, must measure the time lag every time the person to operate the camera or the shooting conditions change. Moreover, even the picture taken with due consideration given to the release time lag is not always a picture picked up at a desired timing or shutter chance.
To allow the operator of a digital still camera to surely take a picture at a desired timing, the camera may be constructed to continuously pick up a desired scene while sequentially recording the resulting successive pictures in a memory in the same manner as a movie camera. However, simply picking up successive pictures and storing the whole data representative of the pictures not only wastes the limited capacity of the memory, but also increases processing loads. This makes it difficult to implement a digital camera capable of producing high-quality still pictures.